This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A183812 #7 Jul 22 2025 09:12:01 %S A183812 1,162,163208,1042063656,41531687999736,10425296660739253420 %N A183812 1/81 the number of (n+1)X(n+1) 0..2 arrays with no 2X2 subblock being a reflection across the shared element pair of any horizontal or vertical neighbor. %C A183812 Diagonal of A183819 %e A183812 Some solutions with upper left block zero for 3X3 %e A183812 ..0..0..2....0..0..0....0..0..2....0..0..0....0..0..2....0..0..0....0..0..0 %e A183812 ..0..0..0....0..0..1....0..0..1....0..0..2....0..0..2....0..0..1....0..0..1 %e A183812 ..2..2..0....0..1..2....1..1..1....1..1..1....1..2..1....2..0..1....1..2..1 %K A183812 nonn %O A183812 1,2 %A A183812 _R. H. Hardin_ Jan 07 2011